TJ Bowl and Hammil Bowl - Wind effects, windslab tests

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SNOWPACK OBSERVATION
TJ Bowl and Hammil Bowl
Submission Info
Forecaster
Friday, January 12, 2018 - 12:30pm
Red Flags: 
Whumphing noises, shooting cracks, or collapsing
Obvious avalanche path
37° 34' 34.5576" N, 119° 0' 15.84" W
Snowpit Observations
More detailed information about the snowpack: 

Toured up from Tamarack to TJ Bowl and Hammil to check on how windslabs were stabilizing in the alpine from Wednesday's winds, and to get an idea of the entire snowpack at higher elevations.  

In the TJ Bowl vicinity, many hand pits failed with light to moderate force in the treeline to 11,000' in the alpine.  See attached video ~10,100' elevation near tree line.  Pencil hard windslab ontop of Fist+ looser fragmented/decomposing storm snow.  Failed a few centimeters below firm windslab.  In the exposed upper slopes, snow surfaces were a patchy mix of very firm windslab, wind crust, and textured soft snow.  In a couple locations ~10,500'+, shooting cracks were observed to go about 1.5m when skinning above unsupported areas (above skin track after kick turn for example).   Pit dug at 10,650', NNE facing slope, see attached profile and picture.  ECT tests failed upon isolation below the ~8cm thick P hard windcrust/slab at surface.  CT tests failed around a thin deeper older windcrust with hard force, Q2, and ECT tests failed as well, but did not propagete (see attached profile).  Facets in the bottom half of the snow pack in this deeper wind deposit area (185cm) were definitely rouding.  

In the Hammil Bowl vicinty there was lots of evidence of many D1.5 avalanches that likely ocured during the storm on Tuesday, or perhaps during the increased wind transport that occured on Wednesday.  Much of the debris and bed surfaces had evidence of wind effects.  No recent slide activity.  For whatever reason, windslabs and surfaces were firmer and harder and more widespread above Hammil than TJ.  They failed cleanly in hand pit tests, but generally required hard force.       

A few locations at mid to lower elvations, whoomphs were heard.  Dug a pit nearby one of these lower elevation whoomphs on a N facing slope at 8960'.  Pit revealed lots of melt/freeze layers with faceted loose layers in between.  One compression test failed: CT14Q2 in a 5-8cm thick layer of looser facets in between the second and third melt/freeze crust down at 50cm below the surface.  Total snowpack depth here in widely spaced trees: ~80cm.  ECT tests did not fail.  

All aspects up to ~9500'+ had atleast a thin melt/freeze crust in the morning.  Slopes at this elevation and below around 3:00pm had melted, and had begun to refreeze.  

Clear sunny warm day with light northerly winds at ridgetops.  1deg C at noon at 10,650'.  

Overall impression:  Isolated windslabs above tree line could still be sensitive to human triggering (overall unlikely, but possible!), resulting in a small avalanche, which could be enough to knock someone off their feet and slide for life down firm slopes, but would unlikely be enough to bury someone.  It's important to poke around in the snow yourself, do your own handpits, as variability always exists between areas and slopes, and even across a slope.   

 

Snowpit or crown profile photo or graph: 
Snowpack photos: 
Snowpit videos (tests, etc): 

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